Conning motor hub surface apparatus for hard disk drives

ABSTRACT

A disk mounting hub has a disk-mounting face formed at one end as a truncated conical surface of revolution symmetric about a central axis. A cylindrical inner hub member is coaxial with the hub body outside diameter and the surrounding mounting face. The inner hub member is adapted to receive a planar disk with a central opening. The mounting face is disposed at a hub face angle (n/2+/−1) relative to the central axis. Hub face angle Ω is selected so that a disk clamping force F applied to an inner disk portion surrounding the opening bends a portion of the disk interior to the hub inside diameter to conform with the conical disk-mounting face. This interior bending portion reduces or eliminates the tendency of the outer disk portion to form an excessive conning angle Φ.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/145,908,filed Jun. 3, 2005, which is divisional application of U.S. patentapplication Ser. No. 10/657,351, filed Sep. 8, 2003.

FIELD OF INVENTION

The present invention relates to a structure and method of mountingdisks on a disk drive spindle to reduce disk conning distortion.

DESCRIPTION OF RELATED ART

One of the primary goals of ABS (air bearing surface) design on a headslider in hard disk drive applications is to maintain a constant flyingheight along the actuator stroke path between inward and outward datazones on a flat disk surface. The disks on a drive spindle are typicallymounted between circular spacers, or rings that apply compressive forcearound the inner periphery of opposite sides of the central diskportion. The compression or clamping force is chosen to keep the diskfrom slipping under the severe operating and environment conditions,such as high start and stop torque, high rotation speed, thermalcycling, thermal expansion, and physical shock and vibration. Theclamping force typically required to prevent disk slippage under suchsevere environments frequently cause mounted disks to deform from aninitially flat plane into non-planar shapes that compromise performance.

Over it is known that even when disks are nominally flat (planar) whenreceived from a disk manufacturer, variations in manufacturing processesproduce disks that have variations in the radial morphology (shape)around the central interior. In the past, the specifications for disksdid not address the issue of disk morphology in a way that wouldguarantee uniform and consistent planarity (flatness) behavior whenmounted on a disk spindle. Some disk manufacturers supplied disks withexcessive rounding (roll-off) or bumping (ski-jump) at the innerdiameter of the disk that would result in unacceptable disk distortionwhen mounted and clamped onto a disk spindle. Disks with such initialradial morphology variations frequently exhibited undesirableperformance variations that caused lower yields and higher costs forfinished disk drives. These conditions persisted until performance andcost requirements reached levels that made them intolerable. Once theinfluence of disk clamping forces and disk morphology on disk distortionwas understood, measurement techniques and disk specifications evolvedto eliminate limitations caused by clamped disk distortion or at leastto reduce the distortion and variation to a level that allowedacceptable performance and yield targets to be met.

However, as performance and cost pressures continue to increase even thepreviously acceptable levels of disk distortion are becoming problematicand in some cases have become unacceptable. Referring to FIG. 1 there isshown a prior art disk hub 100 and an initially flat, planar disk 102with opposite plane, parallel faces. The disk hub 100 has an essentiallyflat, circular mounting face 104 disposed coaxial with spindle axis 106.A coaxial inner portion of the disk is mounted against a matchingco-planar mounting face 104 of the hub. Although the disk and hub facemay initially be perfectly flat when brought into contact, applying asignificant clamping force distribution (indicated by arrows F) againstthe opposite side of the disk to hold the disk (or disks, in the case ofa multiple-disk assembly), can cause the initially planar disk 102 todeform into a concave (downward facing) cone extending beyond the outerdiameter of the hub body as shown by dashed lines 108. The deformedcone-shaped disk 108 has a conning angle Φ that depends on the magnitudeand distribution of the force F and the inner and outer diameters of thehub face 104. For the purposes of this document, the term conning anglerefers to the least angle of inclination between a radial along thesurface of a cone and a plane perpendicular to the cone's axis ofrevolution.

FIG. 2 is a reproduction of FIG. 19 from a document titled Model 4224Disk Inspection Tool Equipment Capabilities published by THôTTechnologies, Inc. of Campbell, Calif. FIG. 2 shows the results of ameasurement of radial and circumferential distortion for an initiallyflat disk mounted on a conventional flat surface hub face.

It is clear that the best-fit cone shows a substantial amount ofdistortion, i.e., an appreciable negative conning angle.

FIG. 3 illustrates the opposite effect of a positive conning angle if(concave upward) for a different clamping force distribution F, causingthe disk 102 to deform into the upward concave conical shape 306.

These situations have been observed in practice over the years, but havemore recently become problematic as disk performance requirementscontinue to increase.

It is known that static loss or gain of head flying height occurs due tosuch crown and camber effects and sensitivities in ABS drives. It isalso known that the geometric disk conning angle can play a role assignificant contributor to crown effect in high performance disk drives.This can result in a noticeable non-uniform radial flying height patternfor ABS drives nominally designated as “constant flying height ABS”.

This loss or gain of flying height due to the crown effect can bemodeled as directly proportional to geometric circumferential curvature.At a certain radial location of the disk, this curvature is simplyproportional to the reciprocal of the radial location and proportionalto the constant disk conning angle for a given disk surface. That is,Static Head Flying Height Gain is proportional to Θ/r where Θ is thedisk conning angle, (positive on convex side, negative on concave side)and r is the radius of a location on a mounted disk.

Moreover, when using mirror ABS design for upward and downward facingheads on two opposed faces of a disk, the disk conning angle causes thegradient and the magnitude of the radial flying height change to be ofopposite signs on opposite faces of the disk.

The signs are opposite, because one side of a cone is concave (sinkingloss) whereas the other side is convex (floating gain). The oppositeradial patterns induced from this difference in terms of both gradientand magnitude may cause significant difference in flying height for twoup- and downward facing heads. This in turn can cause extreme difficultyin attempting data zone layout optimization for balanced performanceamong both the zones and two disk surfaces if the mirror ABS design isadopted. Practically, for instance, 0.08 degree of the conning angle maycause the above problems and 0.02 degree may be small enough to preventthe problematic zoning optimization.

It would be advantageous to provide means for reducing or eliminatingconning angle distortion caused by disk clamping forces.

SUMMARY OF INVENTION

The invention discloses a structure and method for flexible control andadjustment of a desirable disk conning angle by controlling the shape ofthe spindle motor hub surface, on which one or more disks are mounted.In one embodiment of the present invention, a concave conning hubsurface can be achieved by upward micro tapering. For instance, in anapplication with about 200 pound clamp force and aluminum disks withabout 0.05-inch thickness and 3.5-inch diameter, the required typicalrange of the concave (upward) hub face angle is from about 0.01 to about0.03 degree for less than about 0.02-degree convex (downward) diskconning angle.

In the same manner, excessive concave (upward) disk conning angle can bealso controlled by designated convex (downward) motor hub face-angles.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment of the present invention is further described inconnection with the accompanying drawings, in which:

FIG. 1 is a cross-section elevation view of a prior art disk-mountinghub and mounted disk where clamping force causes a negative (downward)conning angle.

FIG. 2 is a display of measured disk conning distortion caused byclamping force in a prior art disk-mounting hub.

FIG. 3 is a cross-section elevation view of positive (upward) conningangle distortion caused by a different clamping force distribution in aprior art disk-mounting hub.

FIG. 4 shows a cross-section elevation view of a disk-mounting hubhaving a micro-tapered disk mounting face in accordance with the presentinvention.

FIG. 5 illustrates a disk aligned and mounted on the hub of FIG. 4.

FIG. 6 depicts a disk aligned and mounted to an alternate micro-tapeddisk-mounting hub in accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is provided to enable any person skilled inthe art to make and use the invention and sets forth the best modepresently contemplated by the inventors of carrying out the invention.Various modifications, however, will remain readily apparent to thoseskilled in the art, as generic principles of the present invention havebeen defined herein.

Reference will now be made in detail to a presently preferred embodimentof the invention as illustrated in the accompanying drawings.

In a preferred embodiment of the present invention, as best seen in FIG.4, a disk mounting hub 400 has a cylindrical hub member 401 with insidediameter 402 extending from one end of the hub body. Disk mounting hub400 forms a cylindrical outside diameter 404 coaxial with member insidediameter 402 along spindle axis 406. Between the inner member insidediameter 402 and the outer body outside diameter 404 there is defined amicro-tapered disk mounting face 408. Face 408 forms a transversesection of a concave (upward opening) conical figure of revolutionsymmetrical with hub axis 406. The hub disk mounting face 408 isdisposed at hub face angle Ω, referenced to a perpendicular to axis 406.

The mounting face 408 is precisely formed, for example, bymicro-machining means known in the art, to a uniform conical surface ofrevolution about the axis 406 to define the hub face angle Ω. The diskmounting hub 400 may be made from a hub material, which may preferablybe aluminum or steel.

With regard to FIG. 5, disk mounting hub 400 is shown receiving a flat,two-sided planar disk 500. The two faces of the disk 500 define acentral disk opening with coaxial inside diameter 502 and an outer diskperiphery with coaxial disk outside diameter 504.

The disk 500 is disposed perpendicular to the axis 406 with a proximalsurface facing the disk mounting_hub 400 and oriented with disk insidediameter 502 aligned coaxial with and fitted around the cylindrical-hubmember 401 inside diameter 402.

An example disk clamping force distribution, as in FIG. 1, indicated byarrows F, is directed against the disk at its opposite, distal side overan inner portion 503 of the disk 500, toward the hub mounting face 408.Clamping force F is coupled from the proximal end of hub member 401 by adisk clamp adapter (not shown) fixed to the proximal end of disk insidediameter 502. Such disk clamp adapters are well known in the art.

For example, one known disk clamp adapter has the form of an invertedaxially symmetric cup with a rigid central mounting base joined aroundits periphery to a depending coaxial rim through an axial-acting springwall. The clamp base is fixed to the proximal end of the cylindrical hubmember 401, for example, by screws, and adapted to press the cup rimagainst the outer face of the inner disk portion 503 with clamping forcedistribution F.

The hub face angle Ω for particular hub geometry and clamping forcedistribution F, is selected so that the bending of the inner diskring-shaped portion (dashed lines 503) of disk 500 bends toward the face408, following the slope of the hub face angle Ω between the hub outsidediameter and inside diameter. The bending of the ring-shaped portion 503toward the face 408 creates a circumferential bending moment acting onthe outer disk portion (503-504) which opposes the tendency of the disk500 to distort into a convex cone under the force distribution F (as inFIG. 1) but instead urges the outer disk portion extending from the huboutside diameter to disk outside diameter to remain exactly or nearlyflat, i.e., perpendicular to the central axis 406 within an acceptablelimit disk conning angle Φ_(min).

In one example of the present invention, for instance, in an applicationwith about 200 pound clamp force F and aluminum disks with about0.05-inch thickness and 3.5-inch outside diameter, the required typicalrange of the concave (upward) hub face angle Ω is from about 0.01 toabout 0.03 degree for less than about 0.02-degree convex (downward) diskconning angle Φ.

An experimental method to select the preferred hub face_angle Ω forparticular conditions, e.g., the above application condition is providedby measuring radial disk slope and differences in bit-error-rate (BER)for opposed heads on a hub-disk assembly as a function of clampingpressure with different hub face angles, and selecting from that data anoptimal hub face angle for minimum disk conning angle distortionΦ_(min).

FIG. 6 depicts an alternative embodiment of the present invention inwhich conventional flat hub mounting face geometry and clamping force Fdistribution as in FIG. 3 would normally cause an excessive positivedisk conning angle Φ. In this case hub face 600 is micro-tapered to apositive hub face-angle Ω₂ so that the disk conning angle is betweenzero and an acceptable limit disk conning angle Φ_(min).

The preferred embodiments described herein are illustrative only, andalthough the examples given include much specificity, they are intendedas illustrative of only a few possible embodiments of the invention.Other embodiments and modifications will, no doubt, occur to thoseskilled in the art. The examples given should only be interpreted asillustrations of some of the preferred embodiments of the invention, andthe full scope of the invention should be determined by the appendedclaims and their legal equivalent.

1. A disk mounting hub for mounting a disk on an axial hard disk spindlein which said disk has opposite parallel faces between a disk outsidediameter and a coaxial disk inside diameter defining a central openingthere through, as a product of the process comprising the steps:defining a rigid cylindrical hub body having a hub outside diameterdisposed along a central axis; defining a cylindrical disk-mountingmember disposed coaxial with said central axis at one end of said body;defining a coaxial member to extend proximally with an inside diameterfrom said one end of said body; sizing said member inside diameter to bereceived through said disk opening; defining a coaxial hub faceextending between said hub outside diameter and said member insidediameter adjacent to said one end of said hub as a truncated conicalsection of revolution symmetrical about said axis, in which said conicalsurface is disposed at an oblique hub face angle Ω relative to saidaxis; and wherein said hub face angle Ω acts to minimize a disk conningangle D when said disk is clamped to said hub face.
 2. The disk mountinghub of claim 1, wherein said process further comprising the step:selecting said angle Ω so that: with said disk mounted perpendicular tosaid hub axis and fitted with said disk inside diameter around saidmounting member inside diameter with one disk face proximal and adjacentto said hub face; and a predetermined clamping force F applied towardsaid hub face from said opposite disk face over an interior centralportion of said opposite disk face; then said interior central portionof said disk bends toward essentially conical contiguity with saidtruncated conical hub face surface at said oblique hub face angle 0 andaway from parallel to the remaining exterior portion of said disk, whilesaid remaining exterior portion of said disk remains disposed within anacute disk conning angle Φ limit relative to a perpendicular to saidaxis.
 3. The disk mounting hub of claim 1, wherein said oblique hub faceangle Ω is selected to form a hub face having a convex conical surfacecontour.
 4. The disk mounting hub of claim 1, wherein said oblique hubface angle Ω is selected to form a hub face having a convex conicalsurface contour.
 5. The disk mounting hub of claim 1, wherein said diskmounting hub is defined from materials are selected from the groupconsisting of aluminum and steel.
 6. The disk mounting hub of claim 1,wherein said process further comprises: a step in which a clamping forceF is applied to said opposite disk face by a clamping member attached toa hub-mounting member.
 7. The disk mounting hub of claim 1, wherein saidprocess further comprises the step: providing a hub-mounting clampmember to include an axial-acting spring member between a disk contactend in contact with said opposite disk surface and a rigid base endmounted to a hub mounting member at its extreme proximal end whereinsaid hub-mounting clamp member is arranged to exert a clamping force Fon said disk surface toward said disk mounting hub.
 8. The disk mountinghub of claim 1, wherein said hub face angle Ω acts to minimize a diskconning angle Φ when said disk is clamped toward said hub face.
 9. Ahard disk drive, comprising: said disk mounting hub of claim 1 couplingto said disk.
 10. The hard disk drive of claim 9, comprising: said diskmounting hub of claim 1 coupling to said disk.